I do not see why this needs to be exposed, especially since device_context is on its way out.
If it were to stay we should need to design an API to manage these factories.

I.e. hold then in a dictionary and provide functions to retrieve the list of keys for the registered factories, to add a factory to this list with some key, to remove a factory by its key.

Even then, these function would belong to dpctl.utils namespace, rather than dpctl.

@PokhodenkoSA If we can avoid adding the function here, let us do it. It just adds more clean up for future.

@oleksandr-pavlyk Given that the changes need to make it to 0.12, I am willing to let it slide. Once, device_context is gone a whole lot of things will have to be deprecated and removed. Basically, all the functions (get_current_queue and family) above nested_context_factories.

I.e. hold then in a dictionary and provide functions to retrieve the list of keys for the registered factories, to add a factory to this list with some key, to remove a factory by its key.

The factory is a key. So we can use list. Also I think we should not guaranty order of contexts.
Agree about functions. But I do not want to make API, especially when users will only append nested context once and will not remove it at all - that is the main use case.

belong to dpctl.utils namespace, rather than dpctl

Partially agree that this is utils. But I think this should be close to device_context namespace. Ideally: dpctl.device_context.add_nested_context_factory(factory).

Once, device_context is gone a whole lot of things will have to be deprecated and removed.

Separate discussion needed: How to make numba redirect context active for compute follows data?

Basically, all the functions (get_current_queue and family) above nested_context_factories.

Agree. As they are located close to each other, so clean up will be easy and in the same time.

If we can avoid adding the function here, let us do it.

I think list is simple enough. @oleksandr-pavlyk let me keep things as is. I know that API should be good isolation. But in this case I would like to be simple.

See Keep a Changelog